sedimentary

Chert (specifically Tan Chert)

Chert (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, beige, or yellowish-brown; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Tan, beige, or yellowish-brown
Luster: Dull to waxy

Identified May 7, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, beige, or yellowish-brown; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed primarily through the chemical or biochemical precipitation of silica (SiO2). It often occurs as nodules or layers within carbonate rocks like limestone or chalk, often during the Paleozoic or Mesozoic eras.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges. Today used as road base, construction aggregate, and occasionally for decorative landscaping or geological collections.

Geological facts

Chert is essentially the same mineral composition as quartz but with a much finer grain. Varieties include flint (usually darker) and jasper (usually red). It was the primary material for prehistoric arrowheads and scrapers.

Field identification & locations

Identify in the field by its characteristic shell-like (conchoidal) fracture pattern and the fact that it is hard enough to scratch glass. It often feels smooth or waxy to the touch localized to the broken surfaces.